The objective of this proposal is to study the molecular mechanisms involved in the translation of genetic messages in a mammalian cell. The translation process requires interaction between messenger RNA, ribosomes, transfer RNA's, Mg ions and several enzymic protein factors. It is the aim of this research to analyze different translational components and define their roles in protein synthesis. The near term objective of this study is to gain a better understanding of the mechanism involved in initiation of peptide chain synthesis in a mammalian cell, namely rabbit reticulocyte. Recently, we described partial purification and properties of several ribosomal factors that are involved in protein synthesis initiation in this system. In this research, we propose to further purify these factors and define their roles in the overall process of peptide chain initiation. Also included in this research are studies on the mechanism of protein synthesis inhibition by antibiotics and anticarcinogens. It is proposed to study the effects of these inhibitors and define their specific locus of action in the protein synthesis machinery.